A prior art drill rig 10 of the general type used for drilling is illustrated in FIG. 1. Drill rig 10 includes a derrick 11 located over a well head 13 and a hoist identified generally as 12 for supporting and lifting a drill string. In the illustrated embodiment, hoist 11 comprises a draw works 12A which is connected to lift a travelling block 12B by a cable 12C which extends over a crown pulley 12D. Draw works 12A can be operated to raise or lower travelling block 12B.
Travelling block 12B is coupled to a top end of a drill string 14 made up of tubular sections 14A. Drill string 14 may be many thousands of feet long. Consequently, hoist 12 must have a very large capacity. Travelling blocks having rated capacities of 250 to 750 tons are not unusual. Components coupling the travelling block to the drill string have similar capacities.
In a traditional drill rig, the drill string is rotated by a rotary table driving a kelly coupled to the top end of the drill string. An upper end of the kelly is coupled to the traveling block by a swivel. Overhead equipment connections used for kelly/swivel/rotary table operations use a traveling block equipped with a hook. The hook can easily be connected to and disconnected from the swivel for drilling and may also support elevator links for tripping. Travelling block—hook connections are made up semi-permanently since it is not generally necessary to disconnect the hook from the traveling block for rig moves.
Most travelling blocks, especially in the larger sizes (e.g. >250 ton capacity), connect to hooks using a becket connection. A becket is a beam which is pinned at either end to the traveling block. Hooks include a member which passes over the becket. Both sides of the interface between the hook and the becket have complementary compound curvatures. There are industry standards (API 8C—Specification for Drilling and Production Hoisting Equipment (PSL 1 and PSL 2), currently in its Fifth Edition) which prescribe compound contact curvatures for becket connections in overhead equipment. These API standards ensure compatibility of components across the industry.
FIG. 2A shows a typical travelling block 20 which includes a becket 22 having ends 22A and 22B coupled to the main body of traveling block 20 by pins 24. A central area 22C of becket 22 has a compound curvature for providing good contact with a hook. FIG. 2B shows a typical hook 26 which includes a bail 28 designed to pass over becket 22 of traveling block 20. Bail 28 has ends 28A and 28B pinned to the main body of hook 26 and a central region 28C which has a compound curvature complementary to that of central region 22C of becket 22.
An alternative way to rotate a drill string is by way of a top drive. Top drives are becoming preferred over kelly/rotary table drives for many drilling operations. A top drive couples to the traveling block and directly drives a top end of the drill string. When a top drive (TD) is used, a hook is neither required nor desirable. A hook adds length, weight, cost, and maintenance. It is therefore common to connect top drives directly to the traveling block, without a hook.
A top drive must typically be disconnected from the travelling block for rig moves, rig up and sometimes also for maintenance. To achieve this it has been necessary to unpin one end of the becket on the traveling block, slide a member of the top drive over the becket and then reinstall the becket. This is difficult and potentially dangerous work that is often performed 20 feet or more above the rig floor without a proper work platform. The components are heavy and can be seized in place by corrosion. To give a sense of scale, a becket pin (removal required for rig up), from a typical 500 ton capacity traveling block, weighs approximately 70 lbs. (30 kg). The becket itself, for a typical 500 ton capacity traveling block, weighs about 750 lbs, (about 350 kg), far beyond human lifting capacity for even one end. Becket pins are typically removed using a hammer and punch bar (a 2 man operation). Once the becket pin is removed, there is no good way to lift the becket—no lifting eyes for winch attachment.
In some cases, the travelling block must be pulled to one side or another to engage the top drive. In such circumstances the becket often does not have enough room to cleanly swing under the bail of the top drive. Coupling the top drive to the traveling block in such circumstances can require moving the top drive to the side and, in coordination with that movement, lifting the becket to engage under the bail of the top drive.
There is a need for a better way to couple components of hoisting equipment used in drilling operations, particularly to couple top drives to traveling blocks. Preferably in a way that provides compatibility with legacy equipment. Preferably in a way that provides some angular flexibility.